A notch filter receives an input signal and allows most frequencies to pass through the notch filter while attenuating frequencies in a specific range (i.e., in the notch) to very low levels. FIG. 1 is an illustration of a block diagram of a conceptual implementation of a notch filter 100 that is helpful in understanding the operation of a notch filter. The example conceptual implementation of the notch filter 100 includes a high pass filter 102 and a low pass filter 104. The high pass filter 102 transmits the input signal Vin above a certain frequency and contributes the high frequency portion of the input signal Vin to the output signal Vout. The low pass filter 104 transmits the input signal Vin below a certain frequency and contributes the low frequency portion of the input signal Vin to the output signal Vout. To attenuate a notch of the input signal Vin (e.g., to implement a notch filter), the high pass filter 102 is adjusted to pass frequencies that are slightly higher than the low pass filter 104 attenuates. In other words, when the signals from the high pass filter 102 and the low pass filter 104 are combined, a band of frequencies (e.g., a notch) from the input signal Vin are not included.
There are various difficulties in implementing a notch filter, both as a standalone circuit, such as on an integrated circuit (IC) chip, or integrated with many other circuits, such as on a system on a chip (SOC) IC. Variations in the circuit components cause variations in the frequency location of the notch. Precision amplifiers to reduce offsets consume substantial power, require extensive chip area, and are difficult to implement so that they are compatible with the other circuits on the chip and do not create excessive noise. Traditional notch filter are also incapable of providing a sufficiently high frequency notching frequency.